| Message |
...but with MAP, the MAP system is measuring pressure and temperature. Then the ECU is estimating air density and applying it to engine speed. The three things that change air density are - temperature, pressure, and humidity. The addition of water vapor makes the intake charge less dense because the molar mass of water is less than dry air. A MAP system can't account for that change in air density because it isn't measuring humidity. With MAF, it doesn't matter what the temperature, pressure, or humidity are. The sensor is measuring the actual amount of air mass entering the engine. It just accounts for it based on the change in current of the hot wire. The current or voltage drop is proportional to the mass of air flowing past the wire. It's true that a MAF performs a calculation, but the 0-5v output signal represents air mass entering the engine. MAF units also typically get better gas mileage because they are very accurate at measuring CFM, even at low volumes.
|
 |
